Hi riotvans and welcome to WebmasterWorld [webmasterworld.com]

I'd check in GSC to see whether there are messages about blocked resources as they used to post when responsive sites/mobile friendliness was their objective. They were clear then that css and js files needed to be accessible to evaluate your site. They may have information to help you decide.

In general their Google Lighthouse site is not considered a security risk but if it is blocked then you will not be able to evaluate their CWV analysis of your site - and neither can Google.

PS - If you really need to share an image, please use an image hosting site such as ibb.co for example.

Apparently, our site purposedly block Google Lighthouse for security purpose.

Please share how you did this?

if my site is blocking Google Lighthouse, will it affect how Google ranks my site in terms of core web vitals?

No. The CWV data is sourced from the Google Chrome User Experience Report, i.e. from actual Chrome users. Google does not take its own measurements of the Core Web Vitals, because they wouldn't reflect real-world performance of your site.

Lighthouse is also built into the Chrome browser, so you could use that to get some insight into your metrics and performance.

Not sure what security risk you're defending against, though. It's just a headless browser, and arguably safer than your actual visitors.

@not2easy
I checked GSC and it's still able to detect the site on its "mobile usability". I just find it weird that when checking via Google's Page Speed Insight, it shows the Lighthouse Error:

"Lighthouse returned error: ERRORED_DOCUMENT_REQUEST. Lighthouse was unable to reliably load the page you requested. Make sure you are testing the correct URL and that the server is properly responding to all requests. (Status code: 403)"

But when checking with GT Metrix, it works fine.

@robzilla
I tried generating a report using my Chrome browser's local Lighthouse extension. However, it still returns a 403 error. The site is mostly handling international B2B information, that's why our System Admin is hesitant in allowing such thing as Lighthouse from accessing the site. Although, I have already explained the same thing. It's also weird that GT metrix can scan and record the site just fine.

Also, the reason why I wanted to check this is because they told me that our site is using dynamic pre-rendering and I had to check it via page speed test to see if it works properly.

GT Metrix does not announce itself in the User-Agent, but Lighthouse does (normal Chrome UA with "Chrome-Lighthouse" at the end), so that's probably what they're blocking.

Seems a bit silly to block a tool that could help a developer audit and potentially improve the site. You should always be able to test the live site, I would think.

the reason why I wanted to check this is because they told me that our site is using dynamic pre-rendering and I had to check it via page speed test to see if it works properly.

Note that Lighthouse loads your page just like a normal browser would (in Chrome, the extension steers your browser, in PageSpeed Insights it loads the page using a Google-hosted headless browser), so rendering is going to be identical to what you see when you load the page. All of this has no direct bearing on how the Google search engine will render your pages, that's a completely separate thing.

I agree with everything that Robzilla said. It won't affect your rankings. But there doesn't seem to be a valid reason for doing so.

Keeping things simple is the hallmark of SEO and doing something like this introduces a (remote) potential for something oddball happening sometime in the future.

Good luck!
;)

Roger Montti